Download bilateral variant of sciatic nerve exhibiting intra

DOI: 10.5958/j.2319-5886.3.2.092
International Journal of Medical Research
&
Health Sciences
www.ijmrhs.com
Volume 3 Issue 2 (April - Jun)
Coden: IJMRHS
st
Received: 21 Dec 2013
Revised: 20th Jan 2014
Copyright @2014
ISSN: 2319-5886
Accepted: 22nd Jan 2014
Case report
BILATERAL VARIANT OF SCIATIC NERVE EXHIBITING INTRA-PELVIC DIVISION
*Rejeena P Raj1, Kunjumon PC2, More Anju B3
1
Tutor, 2Professor and Head, 3Associate professor, Dept. of Anatomy, Sree Mookambika Institute of Medical
Sciences, Kulasekharam, Tamilnadu, India
*Corresponding author email: [email protected]
ABSTRACT
Context (background): In case of high division of the sciatic nerve in the pelvis its, common peroneal component
may pierce the Piriformis muscle. This anatomical variant can explain many clinical findings. Aims: Its objective is
to report a case of high division of the sciatic nerve in order to contribute towards better anatomical understanding
of the gluteal region. Methods and Material: Routine undergraduate dissection of a male cadaver revealed bilateral
variation in sciatic nerve. Results: Sciatic nerve is dividing into tibial and common peroneal components in the
pelvis. Common peroneal component is piercing through the piriformis muscle. Tibial component is emerging
between piriformis and superior gemelli muscle. Conclusions: Sciatic nerve variation can lead to a Piriformis
muscle syndrome, inadvertent injury during operations in the gluteal region, failure of sciatic nerve block and/or
sciatic neuropathy. The differences in routes of these two nerve components can explain them.
Keywords: Common peroneal nerve, Pyriformis muscle, Piriformis syndrome, Sciatic nerve.
INTRODUCTION
CASE REPORT
The sciatic is the thickest and longest nerve in the
human body. Normally, Sciatic nerve leaves the pelvic
cavity as a single trunk through greater sciatic
foramina to emerge between piriformis and superior
gemelli muscle.1 Variation in the course of sciatic
nerve may or may not be accompanied by a variation
in the piriformis muscle. 2 In this case report, we want
to present a case of the bilateral high division of the
sciatic nerve. The common peroneal component is
piercing the piriformis muscle. The variation has
clinical application in case of non-discogenic sciatica
or piriformis syndrome.3, 4 It is also a cause for
coccgodynia and pain in hip, groin and buttock.4, 5 The
variation can lead to post-operative nerve entrapment
after total hip arthroplasty.6 The same being the cause
of failure of nerve block to relieve the pain.7
During routine undergraduate dissection, at Dept of
Anatomy, Sree Mookambika Institute of Medical
Sciences, Kulasekharam, Tamilnadu the variation was
noticed. A formalin-fixed male cadaver aged 60 years
whose case history and cause of death is not known
was dissected. Exposure of the gluteal region was done
following classical incision and dissection procedures.
After skin incision and removal of panniculus
adipsous, gluteus maximus was resected as directed in
dissection manual to expose the structures under cover
of it. The variation was noticed on both sides. All
arteries and nerves were dissected and identified. The
same procedure was followed on both the sides.
Ethics: The procedures followed were in accordance
with ethical standards of handling of cadaver for
learning and teaching.
In this case the High division of sciatic nerve has
occurred in the pelvis. At the greater sciatic foramina,
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Int J Med Res Health Sci. 2014;3(2):451-453
tibial component is emerging below the piriformis
where as common peroneal component is noted to
pierce the piriformis as it leave the pelvis to reach
gluteal region. The branches of sciatic did not reunite
in the gluteal or thigh region. The muscular branches
from the tibial component to the hamstring muscles
are seen arising from the tibial nerve. The course,
branches and relations of both nerves in the popliteal
fossa and leg were normal. The piriformis muscle had
a single muscle belly just splitting to allow passage of
common peroneal nerve. (Fig. 1)
Fig. 1: structures under cover of Gluteus Maximus
DISCUSSION AND CONCLUSION
In the anatomy books sciatic nerve is described as a
major nerve from the lumbo-sacral plexus. It is formed
in the pelvis and emerges at the superior border of the
piriformis. It has two components. It’s tibial
component supply to the hamstrings and the common
peroneal to the short head of biceps femoris in the
thigh. The nerve normally divides into these two
terminal branches; tibial and common peroneal at the
upper angle of the popliteal fossa. In the popliteal
fossa the common peroneal nerve is lateral to the tibial
nerve. In the upper 1/3rd the tibial nerve is lateral to
popliteal vein and artery.1 Beaton and Anson have
studied 360 specimens and classified relations of
sciatic nerve or its divisions to the piriformis muscle
into six types. 1- Undivided nerve below undivided
muscle; 2- Divisions of nerve between and below
undivided muscle; 3- Divisions above and below
undivided muscle; 4- Undivided nerve between heads;
5- Divisions between and above heads; and 6Undivided nerve above undivided muscle.2, 4 The
present case belongs to Type 2. (Fig. 1)
The variations of sciatic nerve are reported in different
races and populations with a variable frequency.8-12The
relationship between sciatic nerve and the piriformis
muscle explain the anatomical basis of the origin of
signs and symptoms of nerve compression. In this case
it is known as ‘Piriformis muscle syndrome’. 3 It is
characterized by sensitivity, motor and trophic
disturbances in the region of distribution of trapped
component of the sciatic nerve.3- 5 The sciatic nerve is
also subject to direct injury, compression, and
ischemia. Total hip arthroplasty may involve excessive
distraction of sciatic nerve, hematoma formation, and
dislocation of bony component and prominence of
implanted unit. Any or all of them can lead to sciatic
nerve injury.6
Sciatic nerve entrapment can lead to pain similar in
distribution and nature like sciatica. Nerve irritation
can be due to contraction or myospasm of piriformis.
Ultrasonography, perineurography by Computerised
Tomography and Magnetic Resonance Imaging can
help to distinguish between two and planning of
intervention.13,14 Resection, division or thinning of
piriformis may help to release entrapped nerve.15, 16
The role of lateral rotation will be managed by
obturator internus, superior and inferior gemelli and
quadrates femoris. Non- surgical management of pain
in Piriformis syndrome includes injecting any one of
these or combination of local anesthetic, steroid,
botulinum toxin and stored in the area of the sciatic
nerve in the gluteal region. A guided procedure under
electromyography (piriformis), nerve stimulator
(sciatic nerve) or other imaging techniques will yield
better results than a blind one.7, 13, 14Other conditions
which mimic the presentation are endometriosis,
myofascial pain syndrome, pelvic tumor, spinal
stenosis, and trochanteric bursitis.
ACKNOWLEDGEMENT
We would like to thank our Institution for the material
support and Mr. Ganeshan for back-up.
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